System and method for injecting water into an underwater hydrocarbon reservoir

ABSTRACT

Water is supplied from a host facility ( 2 ) to a pump ( 10 ) in a seabed facility ( 5 ) via a connecting pipeline ( 6 ). The pump ( 10 ) pumps the water to a higher pressure, and injects the pumped water into a hydrocarbon reservoir at a pressure higher than the pressure of the fluid in the reservoir so that it drives production fluid there to the host facility ( 2 ).

[0001] The present invention relates to a system and method forinjecting water into a hydrocarbon reservoir.

[0002] In an oil and/or gas field development, production fluid,extracted from the hydrocarbon reservoir by production wells, is drivento a host facility by the natural pressure of the reservoir. However,the natural pressure varies from field to field and some reservoirs maynot have enough pressure to drive the production fluid to the hostfacility.

[0003] A way of overcoming this problem is to boost the pressure of thereservoir by injecting water supplied from the host facility into it. Aseabed facility pipeline connects the host facility to a seabed facilitywhere the pipeline is manifolded into separate well flowlines connectedto water injection wells located at the extremities of the reservoir.Water for injection purposes is normally chemically treated and filteredat the host facility to ensure its suitability for injection into thehydrocarbon reservoir. However, in some instances, dependent upon thelocal seawater and the particular reservoir, it may be possible toinject seawater into the reservoir without chemical treatment.

[0004] The water is pumped down the seabed facility pipeline and intothe reservoir via the seabed facility, the well flowlines and the waterinjection wells. The injected water is pumped to a pressure higher thanthe natural pressure of the reservoir so that it drives production fluidfrom the reservoir up to the production wells and on to the hostfacility.

[0005] The required pressure of the injected water is typically in theregion of 27.58 MPa (4000 pounds per square inch). Hence, the pipelineand flowlines which are required to convey the injected water to theinjection wells have to have walls thick enough to withstand the highpressure of the water. The costs of the pipeline and flowlinesthemselves and the installation costs are high.

[0006] U.S. Pat. No. 4,848,471 discloses a system for injecting waterinto a production well. Seawater is treated and pressurised at a hostfacility before being transported in a supply line to drive anunderwater fluid driven motor. A portion of the seawater is conveyedfrom the supply line for injection into the well via an injection pumpdriven by the motor. Return water from the fluid driven motor is carriedin a separate return line back to the host facility.

[0007] It is therefore an object of the present invention to provide asystem and method which overcomes at least the above-mentioneddisadvantage of the prior art.

[0008] According to one aspect of the present invention there isprovided a system for injecting water into a hydrocarbon reservoir,comprising a host facility having water supply means, an underwater pumpremote from the host facility, and connected to the water supply meansby a pipeline, and at least one water injection well connected to theunderwater pump, whereby the pump is arranged to pump the water receivedfrom the pipeline to the or each well to inject the pumped water Intothe reservoir at a pressure higher than the pressure of the fluid in thereservoir, characterised: in that

[0009] said underwater pump comprises an electric motor driven pump.

[0010] The pump may be connected to the at least one water injectionwell by at least one flowline which is able to withstand conveyed fluidof a higher pressure than the pipeline between the host facility and theunderwater pump.

[0011] The pump is preferably located at an underwater facility such asa seabed facility. Gravity alone may be used to convey water to the pumpat the underwater facility. In contrast, the prior art describedrequires the water to be pumped to the seabed facility. By locating thepump on the underwater facility, a pipeline able to convey fluid at ahigh pressure is not required between the host facility and theunderwater facility, as water from the host facility is only at a highpressure once it has been pumped by the pump. Hence, the pipelinebetween the host facility and the underwater facility may have its pipewall thickness reduced as it does not need to convey fluid at such ahigh pressure. As there is a reduction in the quantity of pipe materialfor this pipeline, there is a significant cost saving.

[0012] By conveying the water for injection at a lower pressure to theunderwater facility, the pressure losses due to friction in the pipelineare reduced. Consequently, less power is required to pump the water forinjection, enabling a smaller pump and drive motor (which is electric)to be specified at the underwater facility and, if required, at the hostfacility. Hence, there is a further cost saving as a smaller pumprequires less energy to drive it. If the host facility also has a pumpfor water supply, the reduction in size of the pump and its associateddrive motor provides a saving in deck space on the host facility and inthe weight to be supported by the host facility. If water supply is bygravity alone, no pump need be provided at the host facility.

[0013] The reduction in pipe wall thickness enables the sections of thepipe for making up the pipeline to the underwater facility to be weldedtogether more easily and quickly which considerably reduces fabricationcosts. Furthermore, the reduction in pipe wall thickness may enable thepipeline to be reeled onto a drum and be laid from a pipe reel-lay bargewhich is a faster method of installing a pipeline than otherconventional methods.

[0014] The savings in pipeline costs enables longer tie-backs to thehost facility to be economically considered which may allow the use ofan existing host facility to be used for a remote field as opposed tohaving to provide a new host facility. This is of particular benefitwhen the field to be developed is located beneath deep water.

[0015] The system preferably includes a power and control umbilical fromthe host facility to the underwater pump for conveying power and controlsignals to the pump. The power and control umbilical may be alsoarranged to convey power and control signals required for otherunderwater equipment such as wellhead trees and manifolds. Minimaladditional cost is incurred when providing power to the underwater pumpif the same umbilical is used for the underwater pump and otherunderwater equipment.

[0016] The underwater facility may include a retrievable module whichincorporates the pump. Hence, the pump may be easily recovered forinspection, maintenance or repair, for example. The module may be of thetype forming part of the modular system designed by Alpha Thames Ltd ofEssex, United Kingdom, and named AlphaPRIME.

[0017] According to another aspect of the present invention there isprovided a method for injecting water into a hydrocarbon reservoir,comprising the steps of supplying water from a host facility to anunderwater pump via a connecting pipeline, pumping the water received bythe underwater pump to a higher pressure, and injecting the pumped waterinto the reservoir at a pressure higher than the pressure of the fluidin the reservoir, characterised by the step of:

[0018] driving the underwater pump with an electric motor.

[0019] The method may include the steps of using any of the systemcomponents referred to above.

[0020] Embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings, in which:—

[0021]FIG. 1 is a schematic diagram of a system for putting theinvention into practice; and

[0022]FIG. 2 is a modified detail of FIG. 1.

[0023] Referring to FIG. 1 of the accompanying drawings, a system 1 hasa host facility 2 which may be, for example, onshore or on a fixed orfloating rig. The host facility 2 has an injection water treatment plant3 with a connected pump 4 which is connected to a remote seabed facility5 by an injection water supply pipeline 6. The seabed facility 5 isconnected to a plurality of water injection wells 7 for a hydrocarbonreservoir-whereby each well is connected to the facility 5 by a separatesupply flowline 8 which is able to withstand conveyed water of a higherpressure than the water supply pipeline 6.

[0024] At the seabed facility 5 the water supply pipeline 6 is connectedto an inlet 9 of a high pressure pump 10 and a conduit 11 from an outlet12 of the pump 10 is manifolded to the flowlines 8 connected to thewater injection wells 7.

[0025] The pump 10 is arranged to be supplied with power and controlsignals from the host facility 2 via a power and control umbilical 13.

[0026] The operation of the system 1 will now be described.

[0027] The water treatment plant 3 chemically treats the water forinjection so that it is suitable for injection into the hydrocarbonreservoir and the pump 4 at the host facility 2 pumps the treated waterinto the water supply pipeline 6 where gravity assists the conveyance ofthe water to the seabed facility 5.

[0028] At the seabed facility 5, the water is pressure boosted by thehigh pressure pump 10 and is injected into the hydrocarbon reservoir viathe well

[0029] supply flowlines 8 and the water injection wells 7. The pressureof the injected water is higher than the pressure of the fluid in thereservoir so that it drives the production fluid to the host facility 2via production wells (not shown).

[0030] A modification to the system 1 will now be described in whichparts which correspond to those shown in FIG. 1 are designated with thesame reference numerals and are not described in detail below. In themodified system, the seabed facility 16 illustrated in FIG. 2 comprisesa base structure 17 which supports a retrievable module 18 that containsthe high pressure pump 10. The pump inlet 9 is connected to theinjection water supply pipeline 6 from the host facility 2 by amulti-ported fluid connector 19 such as that described in GB-A-2261271and the pump outlet 12 is connected by the conduit 11 to the well supplyflowlines 8 via the same multi-ported fluid connector 19. This connector19 enables the module 18 to be isolated from the pipeline 6 andflowlines 8 connected to the base structure 17 when the module 18 is tobe retrieved.

[0031] In addition, the module 18 has a power and control pod 20 whichis connected to the power and controls umbilical 13 by a connector 21whereby the pod 20 directs power and provides control signals toequipment within the module 18. In particular, the pod 20 controls thehigh pressure pump 10 but it may be overridden by control signalsreceived from the host facility 2 via the umbilical 13. The pod 20 alsodrives the pump 10 with power received from the host facility 2 via theumbilical 13.

[0032] In use, water from the host facility 2 is received by the highpressure pump 10 in the module 18 via the fluid connector 19 andpressure boosted water is pumped out of the module 18 via the fluidconnector 19 and manifold conduit 11 and into the hydrocarbon reservoirvia the well supply flowlines 8 and water injection wells 7.

[0033] Whilst particular embodiments have been described, it will beunderstood that various modifications may be made without departing fromthe scope of the invention. For example, the pump 4 at the host facility2 may not be required if the injection water can flow to the remotefacility 5 under the action of gravity alone. The power and control pod20 in the retrievable module 18 is also optional, as power and controlcould be provided/controlled externally of the module. The pipeline andflowlines described may be of rigid or flexible construction.

[0034] Although the invention has been described in the context of asubsea hydrocarbon field, it would also be applicable to other areassuch as swamps whereby the system including the pump 10 remote from thehost facility 2, would be land based.

1. A system (1) for injecting water into a hydrocarbon reservoir,comprising a host facility (2) having water supply means (3), anunderwater pump (10) remote from the host facility (2), and connected tothe water supply means (3) by a pipeline (6), and at least one waterinjection well (7) connected to the underwater pump (10) whereby thepump (10) is arranged to pump the water received from the pipeline (6)to the or each well (7) to inject the pumped water into the reservoir ata pressure higher than the pressure of the fluid in the reservoir,characterised in that said underwater pump comprises an electric motordriven pump (10).
 2. A system as claimed in claim 1, wherein the pump(10) is connected to the at least one water injection well (7) by atleast one flowline (8) which is able to withstand conveyed fluid of ahigher pressure than the pipeline (6) between the host facility (2) andthe underwater pump (10).
 3. A system as claimed in claim 1 or 2,wherein the pump (10) is located at an underwater facility (5).
 4. Asystem as claimed in claim 3, wherein the underwater facility (5)includes a retrievable module (16) which incorporates the pump (10). 5.A system as claimed in any preceding claim 1, including a power andcontrol umbilical (13) from the host facility (2) to the underwater pump(10) for conveying power and control signals to the pump.
 6. A system asclaimed in claim 5, wherein the power and control umbilical (13) isarranged to convey power and control signals required for otherunderwater equipment.
 7. A method for injecting water into a hydrocarbonreservoir, comprising the steps of supplying water from a host facility(2) to an underwater pump (10) via a connecting pipeline (6), pumpingthe water received by the underwater pump (10) to a higher pressure, andinjecting the pumped water into the reservoir at a pressure higher thanthe pressure of the fluid in the reservoir, characterised by the stepof: driving the underwater pump (10) with an electric motor.